1. Field of the Invention
The present invention relates to a large-sized vinyl chloride seed, a method of preparing the seed, and a vinyl chloride resin prepared using the seed. The vinyl chloride resin exhibits improved high-shear and low-shear viscosity properties through adjustment of the weight ratio of the large-sized vinyl chloride seed and a small-sized vinyl chloride seed with an average particle size of 0.08 to 0.2 μm.
2. Description of the Related Art
A paste vinyl chloride resin is a general-purpose resin that is widely used worldwide for domestic and industry applications, and is generally prepared by emulsion polymerization, micro-suspension polymerization, or seed emulsion polymerization.
In seed emulsion polymerization, seed particles with different particles sizes, generally two kinds of seed particles are used, and the viscosity and other properties of a final product are controlled by adjusting the ratio of the seed particles. In particular, the final particle size of a vinyl chloride resin wholly depends on the particle size of a large-sized seed and the amount of an initiator contained in the seed.
Conventionally, a vinyl chloride resin is prepared from a large-sized seed with a particle size of 0.5 to 0.54 μm and a small-sized seed with a particle size of 0.08 to 0.2 μm, and has an average particle size of about 0.8 to 1.3 μm. However, in case of using a large-sized seed with a particle size of 0.54 μm, it may be difficult to enlarge the particle size of a vinyl chloride resin to a level above a predetermined value. Further, the use of a large-sized seed with a larger average particle size may lead to increased production of abnormal polymer agglomerates (called “scales”) which are not normal polymers. The scales may be recovered in a state of being mixed with a desired polymer product or being attached to an inner wall of a reactor. The scales should be filtered out since they cannot be used as normal products, and more scales may lead to productivity loss and lowered product quality.
A large-sized seed may be prepared by micro-suspension polymerization of monomer droplets obtained by homogenizing a mixture of a vinyl chloride monomer, an emulsifier, and an oil-soluble polymerization initiator using a pressure homogenizer or a centrifugal rotor-stator type homogenization pump. The particle size of a large-sized vinyl chloride seed is significantly affected by a factor such as the amount of an emulsifier, the number of rotation and operation time of a homogenizer, the speed (rpm) of an agitator, and a total solid content (TSC).
Generally, the average particle size of a large-sized seed is controlled by adjusting the amount of an emulsifier. However, when a large-sized seed with an increased particle size prepared through the use of a decreased amount of an emulsifier is subjected to seed emulsion polymerization, more scales may be undesirably produced.